Facilitação como mecanismo promotor de crescimento vegetal: seleção e avaliação de cepas bacterianas

Abstract

Soil is a dynamic system in which organisms interact through direct and indirect relationships.Semi-arid regions present peculiar soil and climate conditions that limit the development ofvarious organisms. Several groups of microorganisms, including actinobacteria and rhizobia,perform essential functions in these areas. Actinobacteria are recognized for their metabolicpotential, while rhizobia directly contribute to the incorporation of nitrogen through thesymbiosis established, mainly, with legumes. Microorganisms can establish differentinteractions mediated by the presence of nutrients and metabolic mechanisms intrinsic to theorganisms. Understanding how metabolic processes influence the adaptive potential ofactinobacteria and rhizobia allows us to understand the mechanisms that generate coexistencein a natural environment. In Chapter I, a reference analysis of studies on dry regions,actinobacteria, rhizobia and metabolic interactions was carried out, related to aspects of themicrobial ecology of terrestrial environments. In chapter II of this work, twenty-seven strainsof actinobacteria and 26 of rhizobia were isolated from rhizospheric soil samples from an areaof the Ubajara National Park - Ce. They were biochemically characterized and tested for theirability to metabolize xylan, pectin and solubilize inorganic phosphate under pHs (4, 5, 7 and9), temperatures of (39° , 41° , 43° and 45° C) and salinity of (1, 2, 3 and 4%). Thebiochemical characterization showed homogeneity in the use of carbon and nitrogen sourcesbetween the strains of the two groups. Actinobacteria and rhizobia strains were able todegrade pectin-containing compounds. Xylan decomposition was observed only in thepresence of actinobacteria UB03. Phosphate solubilization was positive in six strains ofactinobacteria and five of rhizobia, with the highest solubilization index recorded in strainL91. The abiotic variables with the highest correlation with metabolic activity occurred at pHs7 and 9, 1% NaCl and at a temperature of 39° C. In chapter III, the occurrence of metabolicinteraction between actinobacteria and rhizobia and its influence, through coinoculation, onthe development of cowpea (Vigna unguiculata) plants was evaluated. Twenty-six strains ofrhizobia and 23 strains of actinobacteria were co-cultured in vitro in media containing xylan,pectin and calcium triphosphate. Strains of Streptomyces sp (UB05 and UB11) were selectedfor in vivo evaluation of the effect of coinoculation with eight strains of rhizobia(Bradyrhizobium sp) on the development of cowpea. The compatibility between theactinobacteria and rhizobia strains showed a significant difference between the substrates,with the compatibility between the microbial groups being 55.57%, 100% and 90.45% on thesubstrates pectin, xylan and calcium triphosphate, respectively. Coinoculation showedpositive effects on the plant biomass of plants that received treatment with actinobacteria andrhizobia. The association of microorganisms with different metabolic capabilities proved to bea contributing factor to the coexistence of bacteria.